State of Technology Report for Force Main Rehabilitation, Final ...
State of Technology Report for Force Main Rehabilitation, Final ...
State of Technology Report for Force Main Rehabilitation, Final ...
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Figure 6-1. Polyurethane Pipeline Cleaning Pigs<br />
(Photo courtesy <strong>of</strong> Pipeline Pigging Products)<br />
High Pressure Water Jetting<br />
Jetting has become very common, yet is limited in its capabilities. It is currently the most popular<br />
cleaning method <strong>for</strong> gravity sewers and is widely used throughout the world. Jetting machines range<br />
from compact van-pack units <strong>for</strong> cleaning small diameter drains, through trailer-mounted jetters <strong>of</strong><br />
various power ratings, to full tanker-jetters (which may also combine vacuum removal) up to the largest<br />
unit <strong>of</strong> a water recycling facility.<br />
Although high pressure jetting can achieve excellent results if used wisely, it also has the potential to<br />
make a bad situation worse and to create problems where none existed. Jetting a cracked or fractured<br />
pipe may cause the fragments to become loose and fall into the pipe, creating a collapse and a blockage.<br />
Persisting with high pressures in an attempt to remove the blockage can wash away the pipe surround,<br />
resulting in further destabilization and perhaps even subsidence at the surface. Leaving a high pressure<br />
jet in one position <strong>for</strong> more than a few seconds may puncture the pipe or damage the wall, even if the<br />
pressure is below the recommended maximum.<br />
There is some risk in jetting at high pressure in plastic pipes, notably uPVC. Generally, the wall<br />
thickness <strong>of</strong> a solid wall uPVC pipe is such that high pressure jetting is unlikely to cause serious damage,<br />
although excessive pressures should be avoided. The main concern is with structured wall polymeric<br />
pipes where most <strong>of</strong> the strength is provided by external ribs or corrugations, and the inner wall can be<br />
quite thin (sometimes less than 2 mm). Structured wall pipes were introduced to reduce the required<br />
quantity <strong>of</strong> material (and hence the weight and cost) <strong>for</strong> medium to large diameters, while providing<br />
adequate stiffness to resist external loads.<br />
The main drawback <strong>of</strong> high-pressure jetting is that the debris in the sewer can be flushed downstream<br />
rather than being removed. Jetters may be excellent <strong>for</strong> clearing localized blockages, but are less well<br />
suited to dealing with large volumes <strong>of</strong> silt or similar material over long lengths <strong>of</strong> sewer.<br />
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